Paving machines are generally used for laying heated paving material, such as, bituminous aggregate mixtures or asphalt, onto a roadbed. After heated asphalt is laid, it is typically spread, leveled and compacted such that upon cooling, a road with a uniform, smooth surface that becomes passable by vehicles is achieved. In order to spread the heated asphalt, a paving machine, known as a screed, is typically used. Such screeds can be pulled by a tractor, truck or the like or can be self-propelled. The truck or the tractor supplies the asphalt and the screed then heats, vibrates and manipulates the asphalt into a smooth uniform surface. A screed generally employs a screed assembly having one or more screed elements.
Each screed element may have a mechanism for heating the asphalt. Often, screed elements include two main elements provided in the center of the screed, and hydraulically extendable extenders connected to the sides of the two main elements to widen the paving capability of the screed assembly as a whole. In addition to the main elements and the extenders, bolt-on extensions can be connected to the extenders for paving even larger areas. For example, for paving an area greater than five meters, six screed elements including, two main elements, two extenders and two bolt-on extensions may be employed, all of which may be heated as well for ease in manipulating and spreading the heated asphalt.
In order to heat such screed elements, they are generally powered using a generator under control by a control system. The control system directs power to the different sections of the screed elements by reading inputs from temperature sensors located on each of the screed elements. Traditionally, during heat-up of the screed elements, the control system continuously powers (to heat) the two main elements while alternating between the extenders and the bolt-on extensions. Thus, as the main elements reach a desired temperature, power to the main elements is cut-off, while it continues to alternate between the extenders and the bolt-on extensions until they reach the desired temperature as well.
Although the above method of heating the screed elements is effective, it suffers from several disadvantages. For example, the extenders and the bolt-on extensions are only heated at half the power (e.g., because of power switching), while the main elements are heated at full power (e.g., because of receiving continuous power). This causes the main elements to be heated up before the extenders and the bolt-on extensions, resulting not only in extended heat-up time of the screed elements, but also causing potentially cold screed elements and, particularly, cold main elements, which have to wait for the extenders and the bolt-on extensions to reach the desired temperature before being used. It may also result in non-uniform heating of the screed elements, longer paving times and unnecessary power wastage.
It would accordingly be beneficial if an improved mechanism for effectively controlling heating of the screed elements were developed.